Getting a jump on a national movement to expand early childhood education, California Democrats on Tuesday proposed creating universal preschool for 4-year-olds.

The program would be voluntary, just as kindergarten is in California. Over a 5-year phase-in beginning in 2015-16 school year, it is estimated to cost about $1 billion.

But proponents argue that those costs would be offset by savings down the road. They point to studies showing that better preparation for academics would result in fewer children enrolled in costly special-education classes, and fewer students failing in school and ended up in prison.

The state already funds preschool for certain 4-year-olds — those just missing the cutoff date to start kindergarten because they have birthdays toward the end of the year.

SB 837 would make that class, known as transitional kindergarten, available to all 4-year-olds.

“It’s impossible to overstate how important these early years are to a child’s future success in school,” said state superintendent of schools Tom Torlakson, a co-sponsor of the legislation. “Transitional kindergarten — particularly a full-year, full-day program — can make all the difference, especially for families who may be struggling to give their young children these valuable learning opportunities.”